Process for the preparation of iminodiacetonitrile



3,167,530 PRUGESS FQR THE PREPARATKON 9F TMTNUDHACETONTTRTLE KennethWorden Saunders, Darien, William Herbert Mentgomery, Springdale, and.lames Charles French, Stamford, Comm, assignors to American CyanarmdCempany, Stamford, Conn, a corporation of Maine No Drawing. Filed Apr.12, 1962, Ser. No. 186,859 3 Claims. (Cl. Mil-465.5)

This invention relates to the synthesis of nitriles. More particularly,it relates to a novel process for preparing iminodiacetonitrile.

Iminodiacetonitrile has previously been prepared by several differentroutes. A classical procedure for its preparation is the ammonolysis ofglycolonitrile as described by Eschweiler, Ann., 278, 238 (1894). Thisparticular process has been unsatisfactory because of poor yieldsobtained and because of the time required for completion of thereaction.

A better method has been described by Thompson in US. Patent No.2,511,487. This particular procedure for producing iminodiacetonitrileinvolves heating amino acetonitrile with glycolonitrile in the absenceof an alkaline catalyst. This process, however, suffers from thedisadvantage that both reactants must first be prepared by means ofseparate syntheses.

Similarly, the preparation of an intermediate is necessary in theprocess of Mostek in US. Patent No. 2,442,547 which outlines a processfor producing iminodiacetonit'rile from chloroacetonitrile and gaseousammonia.

The necessity for resorting to an intermediate is also found in theprocess described by Bailey in I. Am. Chem. Soc., 39, 938 (1915) whichoutlines the preparation of iminodiacetonitrile by the reaction ofN-methylene glycinonitrile and hydrogen cyanide.

Perhaps the most direct synthesis for making iminodiacetonitrile is thatdisclosed in the recently issued US. Patent No. 2,794,044 to Miller. Theprocess therein sets forth the reaction of ammonia, formaldehyde andhydrogen cyanide in a slightly acidified aqueous solution. This process,however, is essentially a batch proc- ,ess, the time for which may rangefrom ten to twenty-four hours. As a result, it does not readily lenditself to large scale commercial operation. Furthermore, the yield ofiminodiacetonit'rile based upon the amount of formaldehyde employed isnot considered to be at an optimum level.

It has now been discovered that iminodiacetonitrile maybe prepared in adirect one-step synthesis from cheap, widely available startingmaterials which synthesis not only avoids the use of intermediates foundnecessary for certain prior art processes but also eliminates a costlybatch-wise procedure requiring an excessive amount of time forcompletion of the reaction.

In accordance with the present invention, it has been found thatiminodiacetonitrile may be obtained from hydrogen cyanide, formaldehydeand ammonia by critically controlling the mixing of the reactants, themol ratio of each of the reactants, the temperature and pH of thereaction and the residence time of the reactants within a reactionchamber. Essentially, our invention may be said to be based upon theprinciple that hydrogen cyanide, formaldehyde and ammonia may be reactedin a continuous process to obtain iminodiacetonitrile under certaincritically controlled conditions. While continuity of operation in anychemical process is always an objective, it is an achievement which isnot easily realizable.

Patented Jan. 26, 1965 It is primarily for this reason that the processof the present invention constitutes such a radical departure from theprior art procedures for the preparation of iminodiacetonitrile.

According to the present invention, the mol ratio of formaldehyde tohydrogen cyanide and the mol ratio of ammonia to hydrogen cyanide, thetemperature and pH of the reaction mixture are maintained at criticallevels and the feed of all three reactants to a reactor is criticallycontrolled so as to obtain iminodiacetonitrile in a continuous manner inyields previously not considered possible. In carrying out thissubstantially continuous process, an acid-stabilized aqueousformaldehyde solution is first circulated through the reactor and thesystem is then brought to operating pressure. To this solution hydrogencyanide is added and mixed therewith while the pH is maintained belowabout 4. Ammonia is then added to the formaldehyde-hydrogen cyanidesolution and the system is brought to operating temperature. Whenequilibrium conditions are obtained, which is rapid because of theexothermic nature of the reaction, the feed of all three reactants tothe reactor is continued at approximately the same rate, i.e., the molratio of the reactants is unchanged. The pH of the solution of reactantswithin the reactor is maintained at least above 7. During the feed ofthe reactants to the reactor, product solution is Withdrawn continuouslyfrom the reactor at a rate so as to permit optimum and criticalresidence time of the reactants within the reactor. The product,iminodiacetonitrile, is separated by cooling of the with drawn productsolution. Thus, it has been found that conversions of formaldehyde toiminodiacetonitrile as high as 90% and of hydrogen cyanide toiminodiacetonitrile as high as are readily realizable.

In the process of this invention, the mol ratio of formaldehyde tohydrogen cyanide is maintained at approximately 0.6 to 1.0 while the molratio of ammonia to hydrogen cyanide is maintained at approximately 2.2to 4.0.

The temperature of the reaction mixture is maintained within the rangeof from about 35 to 60 C. while the pH of the reaction mixture is kepton the alkaline side, i.e., from about seven to about nine. It has beenfound that residence times of the reactants within the reactor of lessthan about ten minutes are advantageously employed with times of two tosix minutes preferred.

The reaction which takes place in the practice of the process of thepresent invention may be illustrated by the following equation:

While the overall process is not limited to the use of a particular typeof reaction chamber in which the direct one-step continuous synthesis ofiminodiacetonitrile is carried out, it is advantageous to describe theequipment of the type which may be used.

The reaction of formaldehyde, hydrogen cyanide and ammonia was carriedout in a three-stage continuous tubular reactor designed for a fastexothermic reaction. Each reactor stage consisted of a hair-pin loop of4." stainless steel. Thermocouples were placed at the entrance and inthe middle of the reactor. The reactor was surrounded by a jacket towhich water from a steamwater mixer was fed continuouslycountercurrently. The volume of the first, second and third stages was238, 119.5 and 119.5 milliliters, respectively. The valving on thisequipment was such that nine different flow patterns were permissible.Although this set up was called a three-stage reactor and could be usedas such, the

kinetics of the reaction were studied in a single stage reactor whereinthe flow was circulated through the reacinvention may be carried out,the following tabie summarizes the results of various runs, which arenot to be tor while the volume was 238 milliliters. Alternatively,considered as limitative examples.

Table M01 Ratios Conversions (percent) Residence GHZO Run I., C Time inFeed CH2O NHa OHZO to HON to (ruin) (incl/l.) m m 1N GN MGN IN GN MGN 1Iminodiacetonitrile. 2 Glyeinonltrlle. 3 N-methylenc glycinouitrile.

however, the flow could be circulated through the first From the abovedata, it will be seen that optimum and second loops where the volume was477 milliliters. conversion to iminodiaoetonitrile based upon bothform-The design of the reactors limited temperatures to 110 aldehyde andhydrogen cyanide appears to be obtained C. and pressures to 150 poundsper square inch. when the mol ratio of formaldehyde to hydrogen cyanideThe reactants were pumped and mixed just prior to is about 1.0 or less,the mol ratio of ammonia to hydro entry into the first loop of thecontinuous single-step gen cyanide is greater than 2.2 and thetemperature is reactor. .40 to 60 C. At less than optimum conditions, anincreas- The formaldehyde was fed as an acid-stabilized aqueing amountof glycinonitrile is produced. It will also ous solution. Liquidhydrogen cyanide was pumped be noted that a small amount of N-methyleneglycinoniagainst a discharge pressure of 175 p.s.i. and the dischargetrile may sometimes be obtained. system contained appropriate reliefvalves to reduce the While the process of the present invention is wellpossibility of back up of the reactor product into the adapted tooperation in a continuous manner employing hydrogen cyanide feed system.Anhydrous ammonia was a tubular converter under conditions of eitherviscous fed as a liquid from an ammonia storage tank pressurized orturbulent flow, the reaction may also be conducted with nitrogen at 200psi. in a stirred autoclave or other similar type apparatus. Hydrogencyanide and acid stabilized formaldehyde While the present invention hasbeen described in con were first mixed in a T and immediately followingthis junction with various preferred embodiments, it is to be was athermocouple inserted to record any temperature understood that theinvention is not to be limited to rise. In the process of thisinvention, an exotherm such exemplary description and is to be construedbroadupon mixing was not observed at this point thus indicaty andlimited 3 y the following claimsing the absence of any reaction betweenhydrogen cyanide We Claim; and formaldehyde on the acid side whichreaction would Continuous Process for Preparing iminodiacetoh given rigsto th ibilit th t glycolonitrile was .15 nitriie which comprisesbringing into reactive contact for rodu ed i im, Next in line a a i e rotw a period of less than about ten minutes acid stabilized ports ofwhich served as part of the reactor loop described formaldehyde,hydrogen Cyanide and ammonia, maintainpreviously. Theformaldehyde-hydrogen cyanide feed g during Said Contact Pariod enteredthe third port and ammonia entered the fourth (a) the mol ratio ofCHZO/HCN at between about port of the pipe cross. 05/1 and about 1/1;The formaldehyde employed in the process is ordinar- (b) mol ratio ofNHS/HCN at between about ily 1n aqueous solution advantageouslystabilized with 22/1 and about 4/1; mathanohm an from l 8 to commer' (c)the temperature at between about 35 and about cially available solutionscontaining 30 to 40% formaldehyde are preferably employed. Solutionscontaining (d) 3 at greater than 7; formaldehyde in higherconcentrations may also be used with good success, however.Additionally, it is essential comm-1011511wllhdmwmg Product Semi-10R arate to employ formaldehyde which is acid stabilized. Acids feFtwe m nsaid Contact P and isolating immosuitable for stabilization include themineral acids and, dlacetommle from Said Product Solutionof these,phosphoric acid is preferred. In order to sta- A Process as in claim 1in which reactive Contact I bili h formaldehydc hydroge cyanide Streamat is established by adding ammonia to an aqueous solution. 1 about PH 4il it is admixed with ammonia, thg of acid stabilized formaldehyde andhydrogen cyanide. amount of id gensmny Ianggs from about 05 to 3. Aprocess as in claim 2 in which said aqueous soluabcut 0.5%. tion offormaldehyde and hydrogen cyanide prior to the Iminodiacetonitrile isisolated by cooling the product addition of ammonia thereto ismaintained at a P of solution. Thereupon the iminodiacetonitrilecrystallized less than about esagirtngnd it was filtired olfi) Since itt1ordigarfily cfl fi fl References fited by the Examiner impuriies, 1 maye recrys a 12s rom an or 1'" various suitable solvents including loweralcohols suc h as UNITE D STATES PATDNTS methanol, ethanol and the likeor aromatic hydrocarbons 2,405,966 8/46 Loder 260465.5 such as benzene,toluene and the like, A sample f imino- 87 6/ 50 Thompson 260465.5diacetonitrile obtained according to the process of this 2,794,044 5/57Miller 26o 465 5 invention when recrystallized from benzene melted at 74to C. (Literature 0 to C.) CHARLES B. PARKER, Primary Examiner.

In order to illustrate the manner in which the present 75 LEON ZITVER,Examiner.

1. A CONTINUOUS PROCESS FOR PREPARING IMINODICETONITRILE WHICH COMPRISESBRINGING INTO REACTIVE CONTACT FOR A PERIOD OF LESS THAN ABOUT TENMINUTES ACID STABILIZED FORMALDEHYDE, HYDROGEN CYANIDE AND AMMONIA,MAINTAINING DURING SAID CONTACT PERIOD